/* 隐藏默认三角 */
::-webkit-details-marker
  display: none;
::-moz-list-bullet 
  font-size: 0;
  float: left;
.m-side-bar 
  summary
    user-select none
    outline 0
    dt
      line-height 28px
      font-weight 700
      cursor pointer 
      &::after
        content ''
        position absolute
        width: 12px; height: 12px;
        margin: 9px 0 0 4px;
        background: url('./arrow-on.svg') no-repeat;
        background-size: 100% 100%;
        transition: transform .2s;   
  [open] dt::after
    transform: rotate(90deg);
  dd
    position relative
    padding-left 20px
    margin-bottom 3px
    &:after
      content ''
      position absolute
      width 4px
      height 4px
      left 8px
      top 50%
      margin-top -2px
      border-radius 50%
      background blue
    a
      line-height 24px
      cursor pointer
      &.active
        border-bottom 1px solid black 